This invention is directed to a novel thermoplastic copolyester elastomer composition that is modified by alkali metal salts of phenolic compounds.
Thermoplastic copolyester elastomers form a highly useful class of polymers because of their outstanding physical properties. However, it is known that copolyester elastomer compositions generally are not particularly suitable for blow molding because of their low melt strengths. Furthermore, copolyester elastomers containing ethylene terephthalate ester units are known to process poorly because of their slow hardening rate. This problem of hardening rate also exists for soft copolyester elastomers containing a low percentage of butylene terephthalate ester units.
To attempt to overcome these problems, a variety of compounds have been added to the copolyester elastomers. For example, the sodium salts of monocarboxylic acids, such as sodium stearate, can be added to the polymer to increase melt strength and also to increase hardening rate. However, the melt stability of these compositions at processing temperatures is adversely affected, as indicated by a rapid increase in melt index. It is also known to use salts of polymeric carboxylic acids, such as ethylene/methacrylate acid ionomers, as agents to improve the melt strength of copolyesters. These materials serve as nucleating agents in copolyesters with no detrimental effect on melt stability. However, copolyester blends with the ionomer have been found to exhibit phase separation, resulting in the formation of layers when the blend is used in high shear processing techniques such as injection molding or injection blow molding. The resulting layers separate from one another (delaminate) when such nonhomogeneous articles are flexed or stretched, for example. Obviously, such performance is generally unacceptable.
The present invention describes a copolyester elastomer composition that overcomes the above-mentioned deficiencies. The novel composition is blow moldable, melt stable, and hardens rapidly from the melt. It does not exhibit phase separation in high shear processing techniques including injection molding and injection blow molding.